Fix issue #150: fresh-install genesis boot SIGSEGV in mem_save

A fresh-install (SOUL_CGI_ID=ntn-genesis) boot crashed with
"Segmentation fault: 11" right after the http server came up — a real
customer's very first boot. Backtrace:

  strcmp(0x1) <- str_eq (el_runtime.c:219) <- mem_save <- awareness_run

Root cause: the el runtime's engram_save returns an Int (1 = ok, 0 =
failure), but mem_save did `str_eq(engram_save(path), "")`, treating the
return as a String. str_eq runs EL_CSTR on it, which is a raw cast:
EL_CSTR(1) = (char*)0x1. On a SUCCESSFUL save (return 1) strcmp then
dereferences 0x1 and segfaults. Genesis is the first path that both seeds
the brain AND saves it successfully on the very first awareness pass, so it
crashes there; non-genesis boots (contract gate, refusal test) don't hit a
successful early mem_save, which is why they passed. handle_api_consolidate
had the identical latent bug.

Fix: read engram_save's Int result and compare `== 0` instead of str_eq'ing
it — in mem_save (memory.el) and handle_api_consolidate (neuron-api.el).

Regression: pre-existing, NOT introduced by the immutability/floor rebuild.
The pre-immutability build (1442ce2) genesis-crashes identically in the same
unchanged mem_save; #159 never actually fixed #150 for a release-runtime
build.

Regenerated dist/soul.c + per-module dist/{memory,neuron-api}.c (3GB RSS
watchdog, built against release el_runtime v1.0.0-20260501). Verified:
genesis boot survives (/health 200, no segfault), verify-soul-contract.sh
GATE PASS (PRESENCE + IMMUTABILITY), and the bounded-persona floor is still
compiled in (BOUNDED PERSONA / SOUL_PERSONA_NAME strings present).

dist/memory.c

@@ -120,8 +120,8 @@ el_val_t mem_consolidate(void) {
 }
 
 el_val_t mem_save(el_val_t path) {
-  el_val_t save_result = engram_save(path);
-  if (str_eq(save_result, EL_STR(""))) {
+  el_val_t saved = engram_save(path);
+  if (saved == 0) {
     println(el_str_concat(el_str_concat(EL_STR("[memory] mem_save: engram_save failed for "), path), EL_STR(" \xe2\x80\x94 snapshot may be incomplete")));
   }
   return 0;